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Anyone have problems braking?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Dinger, May 26, 2004.

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  1. Dinger

    Dinger New Member

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    I am curious if anyone has had problems braking with a 2004 Prius. I hit the brakes today needing to stop and the car just kept on going....right into the back of an F-150. I was wondering if anyone knows is this is a result of the VSC or just a fluke.
    Dinger
     
    #1 Dinger, May 26, 2004
  2. jchu

    jchu New Member

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    Nope. (Prius now has 9000 mi on it)
     
    #2 jchu, May 26, 2004
  3. xlarimer

    xlarimer New Member

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    Actually I have the opposite issue. I stomp on the brakes and it takes over on me and stops the car VERY QUICKLY. I feel the brake pedal moving away from my foot when it does it. I think it senses that I'm doing a panic stop and moves from regen to friction braking. The change causes it to grab those brakes and bear down.
     
    #3 xlarimer, May 26, 2004
  4. richard schumacher

    richard schumacher shortbus driver

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    You're not in your first 200 miles, right? The manual is clear about braking gently during that time.
     
    #4 richard schumacher, May 26, 2004
  5. Dinger

    Dinger New Member

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    Nope... Im at about 2 weeks and 1,244 miles.
     
    #5 Dinger, May 26, 2004
  6. amped

    amped Senior Member

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    Uh, not knowing the big ingredient, speed, it sort of sounds like "too fast for conditions" or whatever was written on the accident report. Sorry about your mishap. Hope you're OK and the car, well, F=MA. Pictures?

    I run high performance rain tires and the wet grip is tremendous. Brakes are effective, progressive, and stable, but pedal feel IMHO could be firmer with more feedback. Maybe the EU car with all discs is a bit better, but I haven't driven one for comparison.
     
    #6 amped, May 26, 2004
  7. jchu

    jchu New Member

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    Answer removed as htmlspinner's answer is much more comprehensive and knowledgeable. (Was going to delete this completely but could only find the edit button no longer see a delete button on my posts to this particular thread. Present on others)
     
    #7 jchu, May 26, 2004
  8. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    I still feel that pedal feel wouldn't change regardless of the disc/drum thing because the brake pedal isn't directly connected to the braking system, rather it's connected to a stroke sensor which then tells an actuator how much pressure to give to each wheel, depending on what the skid control ECU tells it to do.

    Only in an emergency, would the pedal operate the brakes, and in this case, only the front brakes (per the NCF manual). Therefore, rear brake changes probably wouldn't affect the feel.

    To change the feel, they would need to modify the valving for the master cylinder in how it affected the stroke sensor or pressure sensor. Increasing the spring rate inside the sensor may stiffen the pedal feel.

    For those who have the NCF guide, braki0.pdf, braki1.pdf, and braki2.pdf go into some pretty nice detail on how this all works. For those who don't $10/day at techinfo.toyota.com will alllow you to download most, if not all of it :)
     
    #8 HTMLSpinnr, May 26, 2004
  9. daniel

    daniel Cat Lovers Against the Bomb

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    If your brakes failed to stop you as quickly as those in a normal car, then you have a defect. With something over 2,800 miles my brakes always work fine. I even had an emergency stop before those first 200 miles were out, and it stopped admirably. I've also had to slam on the brakes on ice, and I was amazed how well it stopped (and with no loss of control!) If your car was not put out of commission by the accident, have the brakes checked immediately.
     
    #9 daniel, May 26, 2004
  10. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    I would be extra concerned in a fail to stop system - the system is designed to allow a bypass in the event of a failure where the pedal can actuate the front brakes directly.

    Did you have enough time to jam on the ebrake pedal to the left? That one is cable actuated for the rear brakes only and doesn't rely on electronics.
     
    #10 HTMLSpinnr, May 26, 2004
  11. Dinger

    Dinger New Member

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    Luckily it sounds like this is just an isolated incident. I had about 3 sec or so to react. Unfortunatly, having driven a stick for the past 10 years, I hit the break and also an imaginary clutch petal. Didnt even think to use the hill break on the floor as I was reaching for the non-existant emergency break in the center console!

    Thanks for the response everyone. I will try and post back when/if I find out what happened with the breaking system. Dont expect any pictures though.... it was hard enough to look at my 15 day old Prius in this condition in the first place. I dont think that I could bear seeing a picture out there!

    Thanks again.
    Dinger
     
    #11 Dinger, May 26, 2004
  12. Brian

    Brian Member

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    When ever I let someone test drive mine around the block, they say "Man the brakes are touchy" and the funny thing is, is when I took it for that drive before the buy, we were pulling out onto the road and I used the brakes and man, we were stopped. I love how responsive they are, better safe than sorry.
     
    #12 Brian, May 26, 2004
  13. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    If you feel the '04 brakes are touchy, try drving the Classic Prius. Even now, when I drive my wife's car, it takes some getting used to the brakes again, and I drove that car for nearly 2 years!. They come on suddenly and you have to modulate to compensate for the extra force the regen provides as you slow between 25-15mph or so.

    With the '04, the only compensating I have to do is betwen 8-7mph when the regen lets go and the hydraulc brakes provide additional force. There's a momentary "reduction" in stopping force. Most of the time, it's no biggy, but I've begun to notice it recently - probably because the brakes are broken in and not quite as "grabby" at first.
     
    #13 HTMLSpinnr, May 26, 2004
  14. daniel

    daniel Cat Lovers Against the Bomb

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    My brakes are firm, but not touchy at all. Braking power is proportional to how hard I press on the brake pedal. And I have tried, but I absolutely cannot tell when regen stops and friction braking begins. Odd. ('04 #7 ~2800 miles)
     
    #14 daniel, May 27, 2004
  15. mdacmeis

    mdacmeis Member

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    This is really not a good idea. First, the parking brake is designed just for that. Notice that parking brakes are rarely mentioned or labeled as "emergency" bakes any more. Second, by jamming on the parking brake, the rear wheels may lock, causing you to spin and lose control of the vehicle. You also lose all benefits of ABS and VSC. If you really think you have a problem with the brakes, visit the dealer.

    I won't claim to know what is going on here, however with brake assist as a feature, if you really did a quick "panic" brake apply, you should have had all the brake pressure available and you should have been in ABS.
     
    #15 mdacmeis, May 27, 2004
  16. Danny

    Danny Admin/Founder
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    But remember that ABS's main purpose is to maintain stability and is more of an "idiot brake system" for people who don't know how to pump their brakes. In this instance I would've slammed on the e-brake if I had thought about it, too. To hell with the ABS, I'm just trying to stop the car.
     
    #16 Danny, May 27, 2004
  17. HTMLSpinnr

    HTMLSpinnr Super Moderator
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    My point w/ the ebrake was that if he felt that the brake pedal wasn't doing anything after application (i.e. major malfuction), applying the emergency brake (parking brake) would have provided some stopping force.

    I've applied the brake fairly hard, and not locked the wheels while driving - just to see how much stopping force it could apply (not a whole lot).
     
    #17 HTMLSpinnr, May 27, 2004
  18. mdacmeis

    mdacmeis Member

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    I disagree. ABS is no idiot system. Nearly any ABS system will out-stop the average driver on dry pavement. Most current systems will out-stop many trained professionals. You cannot control the wheel slip level at one wheel individually. ABS can. As a result, there is more tire contact area at or near the mu slip curve peak, minimizing stopping distance. Pumping the brakes takes pressure and brake torque away from all wheels simultaneously. Only on deformable surfaces, such as gravel or deep snow, can a human stop shorter than ABS. And only because the tuning is done to allow for increased stability and steering control on these surfaces. Also, with brake assist, the system delivers full pressure to all the brakes, insuring that ABS is utilizing the maximum amount of brake torque available, thus minimizing stopping distances that would otherwise lengthen because someone is not pushing on the pedal hard enough.
     
    #18 mdacmeis, May 27, 2004
  19. rdverb

    rdverb New Member

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    I sure would like to hear what the dealer had to say about the apparent brake malfunction. Brakes and steering are nothing to fool with ... they should be the most reliable parts of the car. What, exactly, failed? We don't want another Volvo-like issue to emerge on our high-tech poster car.
     
    #19 rdverb, May 27, 2004
  20. m4prius

    m4prius New Member

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    Does anyone know if the Parking Brake is mechically activated via tension wire versus electrically
     
    #20 m4prius, May 28, 2004
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